The idler (intermediate) gear in the drive gears between the engine and transmission must have the end float set during any reassembly. The helical cut of these gears is designed to keep the noise down but also results in a side thrust that if not controlled will destroy the gearbox and flywheel housings. The end float of this gear is set by changing thrust washers with those of various sizes. The total end float should be keep between .003" to .006"

The idler (intermediate) gear in the drive gears between the engine and transmission must have the end float set during any reassembly. The helical cut of these gears is designed to keep the noise down but also results in a side thrust that if not controlled will destroy the gearbox and flywheel housings. The end float of this gear is set by changing thrust washers with those of various sizes. The total end float should be keep between .003" to .006">;BR>
Shim for 1979-on idler gear with .875" pin diameter.

A fairly crucial part of how the idler gear operates is its tolerances and running clearances. End float is a continual problem as folk often ignore it, and because many units left Rover with incorrect (usually too big) clearances.

Assembling the engine to gearbox (transmission) is explained and simplified in this article. Contrary to popular mis-guidance, all BBUs will fit all four-syncro gearboxes. It was only the three-syncro boxes that varied in casting dimensions causing hassles where 1275s were applied to 850/998 gearbox casings. The longer throw and bigger crank and rod assembly dimensions fouled the sculpted areas in the gearbox case,